var read_line = require('readline-sync')
read_line.setDefaultOptions({ prompt: '' })
var read_line = read_line.prompt
let arr = read_line().split(' ') // 得到字符串数组
var longestCommonPrefix = function (strs) {
  if (strs.length == 0)
    return "";
  let ans = strs[0];
  for (let i = 1; i < strs.length; i++) {
    let j = 0;
    for (; j < ans.length && j < strs[i].length; j++) {
      if (ans[j] != strs[i][j])
        break;
    }
    ans = ans.substr(0, j);
    if (ans === "")
      return ans;
  }
  return ans;
};
console.log(longestCommonPrefix(arr))